1. Field of the Invention
The present invention relates to an electrical connection box, and more specifically, to an electrical connection box mounted in an automobile or the like and loaded with electrical components.
2. Description of the Related Art
As vehicles, e.g., automobiles, are expected to meet increasing market requirements for comfortable riding, they tend to require use of increased built-in electric devices, such as an audio system, navigation system, TV set, power antenna, air conditioner, rear window heater, seat heater, power seat, suspension hardness control device, etc.
The built-in electric devices are supplied with electric power from a battery in an engine room through an electrical connection box near the battery and a wire harness. In some cases, excessive current may flow in the electrical connection box if the vehicle body and the wire harness or the like are shorted or if a load such as a motor goes wrong from any cause. The electrical connection box is mounted with electrical components, such as fuses to cope with such trouble and relays that control power supply to the built-in electric devices in association with various operating switches.
The electrical connection box comprises lower and upper casings capable of being combined with each other, an electrically insulating wiring board located between the lower and upper casings and having wires laid in a desired shape on either side thereof, pressure-welded terminals for lectrical connection between the wires and electrical components and connection between the wires, busbars for high-current conduction on either side of the wiring board, an insulating plate interposed between the upper casing and the busbars so that one of the busbars is held between the insulating plate and the wiring board, and the like. The lower and upper casings are fitted with electrical components, such as relays, fuses, external connecting terminals to be connected to the body-side wire harness, etc., which are located individually in given positions.
In order to form a laying groove 3s in which a wire W is laid in a desired shape, the wiring board is formed with ribs 3a and 3b that extend lengthwise and crosswise and are opposed to each other with a given space between them, as shown in the partial perspective view of FIG. 14. Besides, the respective inner walls of the ribs 3a and 3b are formed individually with projections 3p and 3q that are arranged at given spaces and opposed to one another, whereby the wire W is held and prevented from slipping out of the groove 3s. The wire W is continuously inserted into the laying groove 3s to be laid along a predetermined path on the wiring board.
In general, the wire laying operation is carried out by means of an automatic laying apparatus (not shown). More specifically, the leader of the wire W is inserted into a given position in the laying groove 3s by means of the laying apparatus. Subsequently, the wire W is continuously laid with one stroke along the predetermined path, and its trailer is cut. Thereafter, the laid wire is cut at given spots to be divided into sections for desired circuits, and pressure-welded terminals are driven in given positions so that the wire is connected electrically to the electrical components and external connecting terminals for the individual circuits. Further, busbars each having a given shape are attached to wire laying surfaces of the wiring board 3. The busbars serve to distribute high current from the battery or an alternator. The distributed current is supplied to actuators through the laid wire, fuses, relays, etc.
Each busbar is formed of an electrically conductive metal plate. One busbar is attached to the underside of the lower casing that faces a laying surface of the wiring board, while another busbar is attached to one side of the insulating plate. When the electrical connection box is assembled, each busbar is in contact with a predetermined portion of its corresponding laying surface of the wiring board.
The wire is laid with one stroke, as mentioned before, and is cut in given positions so that a large number of independent circuits are formed. In specific positions in the laying groove 3s, therefore, the wire is laid in two or three tiers. In some cases, the top line of the wire may be lifted by its own deflection or by deflection of the underlying line or lines so that it projects above the laying surface of the wiring board. More specifically, if the wire W is laid in tiers in the laying groove 3s, as shown in FIG. 12, its top line often touches a busbar 4b, as shown in FIG. 13. If the electrical connection box assembled with the wire W in contact with the busbar 4b is mounted in a vehicle, the wire W and the busbar 4b are caused to rub against each other by prolonged vibration of the vehicle, so that an insulator-coated portion of the wire W may possibly break and cause a short circuit. This breakage easily occurs in those portions of the wire W which are in contact with the edges of the busbar 4b, in particular.
In general, the wiring board 3 is a molded article formed of a resin material, such as polypropylene, so that its dimensions are subject to dispersion. In some cases, therefore, the width of the laying groove 3s on the wiring board shown in FIG. 14 and the distance between the opposed wire holding projections 3p and 3q are also subject to dispersion. If the distance between the projections 3p and 3q is shorter than a predetermined length, the wire W cannot be fully inserted into the space between the projections 3p and 3q. Therefore, the wire W may be lifted out of the laying groove 3s as it is laid. If the distance between the projections 3p and 3q is longer than the predetermined length, on the other hand, the wire W may be caused to slip out of the groove 3s by vibration or the like without being held between the projections 3p and 3q. In spots where the wire W is laid in tiers, in particular, the wire W is liable to project from the laying groove 3s.
If the busbar, lower casing, upper casing, etc. are attached to one another with the wire W projecting from the laying groove 3s, that portion of the wire W which projects from the groove 3s keeps on interfering with the busbar, as indicated by two-dot chain lines in FIG. 15.
Since the wiring board and the busbar are interposed between the upper and lower casings, the above awkward situation cannot be easily detected once the electrical connection box is assembled.
If the electrical connection box in this state is mounted directly in the vehicle, the wire W and the busbar are caused to rub against each other by the vehicle's vibration, so that the insulator-coated portion of the wire W may possibly break and cause an undesirable short circuit between the busbar and the wire.